Direct gas phase partial oxidation of olefins by molecular oxygen to epoxides is long considered one of the most important reactions in commercial catalysis. Because of the importance of epoxides in the polyurethane industry, many attempts have been made to make epoxides by various means, some of which are commercialized. To produce epoxides from olefins containing more than two carbon atoms most production techniques use hydrogen peroxide or chlorohydrin as an oxidant. European patent (EP-A1-0 930 308) for example describes the use of ion exchanged titanium silicate for the production of epoxides in the presence of hydrogen peroxide, or chlorohydrin as the oxidant. More recently, U.S. Pat. No. 5,623,090 describes a new class of materials that may allow the direct production of epoxides such as propylene oxide directly from the olefin propylene using molecular oxygen, while in the co-presence of hydrogen. In this patent it is claimed that when gold is deposited on titanium, specifically anatase Titanium dioxide the direct gas phase partial oxidation of propylene to propylene oxide takes place.
Though the Au/titanium oxide system is still far from commercialization, and exhibits poor reaction yields, what separates gold from previous known inventions is the higher selectivities observed for the epxidation of olefins with 3 or greater carbons, an example of such being propylene. Silver based catalyst systems, for example, despite showing good yields and selectivities for ethylene oxide production, fail to give high or promising activities for propylene conversion. Subsequent patents since the work of Hayashi and Haruta (see Hayashi et al., Symposium on heterogeneous Hydrocarbon Oxidation, presented at the Div. Of Petroleum Chemistry, 211th National Meeting, American Chem. Soc., New Orleans, La., Mar. 24-29 1996) have therefore mainly concentrated on the use of gold in conjunction with Titanium WO 97/34692-A1, WO 98/00413-A1, WO 98/00414-A1. The exception is patent EP-A1-0 940 393, that employs gold in the co-presence of the element Zr.
Thus, the current understanding of the art is that the number of active species which can aid the partial oxidation of olefinic material is limited. Furthermore DE-A1-4447231 makes reference to the epoxidation power of Vanadium and Molybdenum specifically in the context of alkenes to glycols, polyols and glycol ethers, and not to the product propylene oxide. Similarly, documents claiming the element Molybdenum (PCT/EP97/05449), Vanadium, Tungsten. Chromium, Hafnium, and Tantalum (EP-A1-266 015) or Scandium (U.S. Pat. No. 5,051,395) to be promoters are likewise considered to be not valid in the context of gold based catalyst systems as the materials listed above, for example, Molybdenum, Vanadium and Scanadium are disclosed only in close connection with titanium as co-compounds.
The inventions described herein involve a process for the epoxidation of olefins, using molecular oxygen and hydrogen, characterized in that, as catalyst, a compound comprising gold, preferably in nanometer size, on a support material, in which the support material is comprised of Scandium, Yttrium, Lanthanide, Hafnium, Vanadium, Niobium, Tantalum, Chromium, Molybdenum and/or Tungsten. All catalysts operate free of the element Titanium. These findings are surprising, in light of the fact that in the last three years of intensive research only very few other catalyst systems containing gold have been discovered for the epoxidation reaction of olefins. The invention shows especially in the case of the Niobium and Tungsten systems which are preferred exceptionally high selectivities with respect to epoxidation, with the selectivity surprisingly improving with time. The invention also exhibits good stability of the catalysts over extended time periods.
Another object of the invention are compounds comprising gold, preferably in nanometer size, on a support material, in which the support material is comprised of Scandium, Yttrium, Lanthanide, Zirconium, Hafnium, Vanadium, Niobium, Tantalum, Chromium, Molybdenum and/or Tungsten.
Yet another object of the invention is a method of catalyzing a chemical reaction through conducting said chemical reaction in the presence of a compound comprising gold, preferably in nanometer size, on a support material, in which the support material is comprised of Scandium, Yttrium, Lanthanide, Zirconium, Hafnium, Vanadium, Niobium, Tantalum, Chromium, Molybdenum and/or Tungsten.
Yet another object of the invention is a process for the preparation of the invented compounds, characterized in that, gold particles of nanometer size are deposited on a support material in which the support material is comprised of Scandium, Yttrium, Lanthanide, Zirconium, Hafnium, Vanadium, Niobium, Tantalum, Chromium, Molybdenum and/or Tungsten.
Yet another object of the invention is a process for the preparation of the invented compounds, characterized in that, compounds comprising of gold particles of nanometer size on a support material in which the support material is comprised of Scandium, Yttrium, Lanthanide, Zirconium, Hafnium, Vanadium, Niobium, Tantalum, Chromium, Molybdenum and/or Tungsten are prepared via a sol-gel-process.